Highly stable mixed-phase Cs-Cu-I films with tunable optoelectronic properties for UVB photodetector applications.

Ultraviolet (UV) photodetector plays an important role in military, civilian and people's daily life, and is an indispensable part of spectral detection. However, photodetectors target at the UVB region (280-320 nm) are rarely reported, and the devices detected by medium-wave UV light generally have problems such as low detection rate, low sensitivity, and poor stability, which are difficult to meet the market application needs. Herein, Cs-Cu-I films with mixed-phase have been prepared by vacuum thermal evaporation. By adjusting the proportion of evaporation sources (CsI and CuI), the optical bandgaps of mixed-phase Cs-Cu-I films can be tuned between 3.7 eV and 4.1 eV. This absorption cut-off edge is exactly at both ends of the UVB band, which indicating its potential application in the field of UVB detection. Finally, the photodetectors based on Cs-Cu-I/n-Si heterojunction are fabricated. The photodetector shows good spectral selectivity for UVB band, and has a photoresponsivity of 22 mA/W, a specific detectivity of 1.83*1011 Jones, an EQE over 8.7% and an on/off ratio above 20.

Different Dissolution Molecular Pathways of Azilsartan Crystals with Different Forms Revealed by In Situ Atomic Force Microscopy.

Here, using in situ atomic force microscopy (AFM), the dissolution behaviors and dissolution molecular pathways of two azilsartan crystals, the isopropanol solvate (AZ-IPA), and form I (AZ-I), in pure water and 6-30% poly(ethylene glycol) (PEG) aqueous solutions are revealed. The dissolution behaviors of step retreat and etch pit formation are observed on the (100) faces of the two crystals, with a single step corresponding to one molecular monolayer in crystal structures. Etching rates of pits increase with PEG concentration. Furthermore, our results show that AZ-IPA dissolves by the direct detachment of molecules from the step front to solution. Such a mechanism remains even when the PEG concentration changes. However, AZ-I dissolves primarily by the surface diffusion mechanism involving molecular detachment from the step front at first and then diffusion over the terraces before desorption into solution. PEG promotes the dissolution of AZ-I crystals by favoring the molecular detachment from the step front.

Thermochromism Perovskite (COOH(CH2)3NH3)2PbI4 Crystals: Single-Crystal to Single-Crystal Phase Transition and Excitation-Wavelength-Dependent Emission.

As a potential multifunctional phase transition material, the organic-inorganic hybrid perovskite has attracted extensive attention in recent years. Here, we report the single-crystal to single-crystal phase transition and excitation-wavelength-dependent emission (EDE) of layered perovskite (COOH(CH2)3NH3)2PbI4. Single-crystal X-ray diffraction indicated that the crystal structure changes from layered Ruddlesden-Popper (RP) at 302 K to "X" network composed of face-sharing and corner-sharing [PbX6]4- octahedra at 425 K. The material exhibits thermochromic change from orange to yellow at higher temperature. Considering the thermochromism of the material, we apply it for anticounterfeiting and information encryption. The material exhibits EDE properties with a fluorescence color changing from green to red upon 420 and 546 nm excitation, respectively. Time-dependent density functional theory indicated that this phenomenon is mainly related to the laser-induced crystal structural transfer. Our research shows that the (COOH(CH2)3NH3)2PbI4 crystal has a potential application for multifunctional devices.

Low-Dimensional Hybrid Lead Iodide Perovskites Single Crystals via Bifunctional Amino Acid Cross-Linkage: Structural Diversity and Properties Controllability.

Three-dimensional perovskite AMX3 has great potential in photoelectric applications, but the poor stability is a major problem that restricts its practical application. The emergence of lower dimensional perovskite solves this problem. Here, we have synthesized a group of novel low-dimensional perovskites with diverse structures. Different amino acids were incorporated in the perovskite cage. The formulas of the compounds are (A')mPbIm+2 (A' = COOH(CH2)nNH2, n = 1, 3, 5, 7, 9). These families of materials demonstrate structure-related stability, tunable bandgap, and different photoluminescence. Single-crystal X-ray diffraction indicated that the five materials employ different structure types varying from edge-sharing structures to face- and corner-sharing Pb/I structures by adjusting the number of C atoms in organic cations, and the level of [PbI6]4- octahedral distortion was also identified. The film prepared using these materials with longer carbon chains (n = 5, 7, 9) showed better stability, and they did not decompose within one year at 75% RH, 40 °C. The bifunctional organic ions containing carboxyl groups as spacer cations will form additional hydrogen bonding between perovskite layers, resulting in higher stability of the material. The band gaps of these materials vary from 2.19 to 2.6 eV depending on the octahedral connection mode and [PbI6]4- octahedral distortion level, density functional theory calculations (DFT) are consistent with our experimental trends and suggest that the face-sharing structure has the maximum band gap due to its flatter electron band structure. Bright green fluorescence was observed in (COOH(CH2)7NH3)2PbI4 and (COOH(CH2)9NH3)2PbI4 when excited by 365 nm UV light. A thorough comprehension of the structure-property relationships is of great significance for further practical applications of perovskites.